The present invention relates to a flap assembly particularly adapted for the trailing edge of a wing of an airplane with requirements for relatively short take-off and landing field length.
It is quite common for present commercial aircraft to have single, double or triple slotted flaps that travel in curved tracks. While this arrangement does provide optimum flap positions for take-off and landing with only small low-drag fairings, the flap track supports are heavy and have inherent in-service problems with track wear and jamming. The main problem arises from the line contact of the highly loaded aft-roller on the track. Another arrangement is used in one configuration of the Boeing 747 airplane, where there is a single slotted flap mounted on an overhead four-bar linkage.
Some short to medium range airplanes are equipped with double slotted flaps, mounted from a simple hinge below the wing. This flap configuration is designed to provide very high lift coefficients for landing with take-off lift coefficient and lift-to-drag ratio not being critical. In this particular airplane configuration, the cruise drag of the deep flap support fairings is not too important for the short range mission.
There is need for improvement for mission requirements where there is relatively high gross weight, high altitude, and limited runway length in that there should be an adequately high lift-to-drag ratio for take-off. For a mix of mission requirements, short and long range, with high gross weight and intermediate runway length, intermediate gross weight and short field length, a flap system with the aerodynamic characteristics of the track guided flaps is desirable.
There have been proposals for a flap system having the desirable features of the track guided flaps, while alleviating some of the difficulties associated with such track guided flaps. Specifically, consideration has been given to flap assembly configurations which provide adequate Fowler motion for various flap angles, while requiring only a small flap support fairing with low cruise drag. With regard to prior proposals known to the applicant, the rather sophisticated flap motion is accomplished with an equally sophisticated linkage system. This complexity involves increased expense in terms of manufacturing and rigging. Having a relatively large number of links which act in series increases probability of failure as well as wear in the multiple pivot points. Thus, there remains a need for improved design for flap configuration employing a relatively simple linkage arrangement, while having a desirable mix of advantageous features as indicated above.
A search of the patent literature has disclosed a number of patent, U.S. and foreign, showing various arrangements for deploying the flap members. Typical of these are the following.
U.S. Pat. No. 2,137,879, Ksoll, shows a trailing edge flap system where there is a fore flap and an aft flap. In one of the arrangements, the fore flap is mounted by an upwardly extending four-bar linkage, and the aft flap is mounted from the fore flap by a downwardly extending four-bar linkage.
U.S. Pat. No. 2,155,546, Hill et al, shows a trailing edge flap configuration where a fore flap is pivotally connected to the wing, and an aft flap is pivotally connected to the fore flap.
U.S. Pat. No. 2,289,704, Grant, shows a flap configuration where there are two flaps. The fore flap is hinge-connected to the wing, and there is a slave linkage assembly to achieve slot control and aileron functions.
U.S. Pat. No. 2,404,956, Gouge, deploys a set of trailing edge flaps by means of long screws which, when turned, move the flaps to their extended locations.
U.S. Pat. No. 2,518,854, Badenoch, shows a main flap extended from an overhead four-bar linkage. There is also a smaller intermediate flap which functions as an "interfoil".
U.S. Pat. No. 2,583,405, Youngman, discloses a trailing edge assembly where there is an overhead four-bar linkage for the fore flap. An aileron is added to the fore flap.
U.S. Pat. No. 3,767,140, Johnson, has a relatively complex crank linkage for the main flap. The aft flap moves on a curved track mounted in the main flap.
U.S. Pat. No. 3,799,474, Scharzler, shows a flaperon with two hinged elements that can move either together or separately.
U.S. Pat. No. 3,827,657, Schwarzler, has a main flap which is hinge mounted to the wing. Also, there are two smaller flaps mounted to the main flap.
U.S. Pat. No. 3,874,617, Johnson, discloses a flap configuration such as that which is used on the YC-14 flap system. There are two downwardly extending links that mount the main flap to the wing structure, and the rear link also serves as the forward link for the second flap. A third link interconnects the fore flap with the aft flap. While analysis indicates that the Fowler motion, slot size and flap rotation angles are desirable, the loads on the links and the actuation loads are undesirably high.
U.S. Pat. No. 3,917,192, Alvarez-Calderon, shows leading and trailing edge devices which are hinged with folding trusses for low actuation loads.
U.S. Pat. No. 3,985,319 and U.S. Pat. No. 4,049,219, Dean et al, have trailing edge flap configurations which utilize a four-bar linkage for the main flap. There is a pivot for the aft flap with a slave link mechanism.
French Pat. No. 838,625 employs an overhead four-bar linkage for fore and aft flaps in a trailing edge flap configuration.
French Pat. No. 995,545 employs an overhead four-bar linkage for the main and aft flaps, with one of the links being a common link. An additional pivot point adds aileron-spoiler function.
French Pat. No. 999,786 discloses a trailing edge flap configuration where there is a relatively complex rocker arm linkage for the main flap for flaperon-spoiler functions. There is a simple pivot for the aft flap, and two actuation systems are provided.
German Pat. No. 1,296,527 discloses a flaperon arrangement with two actuating systems.
In view of the foregoing, it is an object of the present invention to provide a flap system for an airfoil of an aircraft, where there is a relatively simple linkage mechanism having a desirable mix of advantageous features.